The present invention relates to the technical field of an image recording method and an image recording apparatus, and more particularly, to an image recording system using a light modulator of two-dimensional arrangement (two-dimensional spatial light modulator) such as a micro mirror array (hereinafter, referred to as “MMA”) or a two-dimensional mirror array device.
Mainly used in a digital image exposing system utilized in various types of printers is a so-called laser beam scan exposure (raster scan) for two-dimensionally exposing a recording medium with a laser beam modulated in accordance with an image to be recorded by deflecting the laser beam in a main scanning direction while relatively moving the recording medium and an optical system in an auxiliary scanning direction perpendicular to a main scanning direction.
In contrast, recently, various types of digital image exposure systems have been proposed which use two-dimensional spatial optical modulators such as a liquid crystal display (hereinafter, referred to as “LCD”) and the digital micromirror device™ (hereinafter, referred to as “DMD”) that are utilized as a display unit in a display, a monitor and the like. In the exposure systems, a recording medium is basically exposed by forming an image displayed by the two-dimensional spatial optical modulator on the recording medium.
In particular, the MMA is advantageous in exposure at high speed because the MMA has a modulation speed (response speed) faster than that of the LCD and moreover utilizes light more effectively than the LCD.
A so-called outer drum type image recording apparatus is known as an image recording apparatus using the two-dimensional spatial optical modulator. As shown in FIG. 8, for example, the outer drum type image reading apparatus is arranged such that an image formed by the two-dimensional spatial optical modulator (MMA) 94 is exposed on a recording medium 92 wound around the outer surface of a rotary drum 90 so as to record an image.
In the image recording apparatus, light from a light source (not shown) is reflected by the MMA 94, and the image carried by the reflected light (the image within the range that can be recorded by the MMA 94 at a time, which is referred to as the image of one frame) is formed on the recording medium 92 through an imaging lens 96, thereby the image 98 of the one frame is recorded.
The MMA 94 is composed of minute mirrors (micro-mirrors) disposed two-dimensionally in longitudinal and lateral directions in a rectangular shape, wherein each micro-mirror corresponds to one pixel, and the image of the one frame described here is composed of the number of pixels as many as the number of the micro-mirrors constituting the MMA.
At this time, the rotary drum 90 rotates in the direction shown by an arrow T in the figure at a constant speed and the recording medium 92 is also rotated in the same direction as that of the rotary drum 90. Thus, the image 98 of the one frame is sequentially recorded on the recording medium 92 from a lower side to an upper side as shown by an arrow M in the figure. The direction M is referred to as a main scanning direction in image recording.
An optical system composed of the MMA 94, the imaging lens 96, and the like is placed on an auxiliary scanning/transportation unit 100 and moved at a predetermined speed in the direction shown by an arrow S that is approximately perpendicular to the (above-mentioned) main scanning direction M. The direction S is referred to as an auxiliary scanning direction.
In the illustrated image recording apparatus, images are recorded on the recording medium 92 by a so-called spiral exposure system as shown by slanted lines in the figure by moving the optical system in the auxiliary scanning direction S in synchronism with the rotation of the rotary drum 90 and by controlling image data to be supplied to the MMA 94.
However, in the image recording system for executing spiral exposure while carrying out areal exposure (exposure of the image of the frame) using the conventional two-dimensional spatial optical modulator described above, frames cannot be aligned with each other when the circumferential length of the drum is not an integral multiple of the size of an image recorded on one frame in the main scanning direction. Accordingly, when images have been recorded by rotating the drum once and then images begin to be recorded in a subsequent one rotation of the drum, the image of one frame recorded in the subsequent one rotation of the drum cannot be located exactly adjacent to the image of one frame recorded in the previous one rotation of the drum, that is, the frame of the former image overlaps the frame of the latter image or a gap is formed therebetween, on the contrary, thereby a problem arises in that streaked unevenness is produced in the main scanning direction.